The study of matter with smaller and smaller dimensions in various fields of science is now leading to orders of magnitude at which it can no longer be considered as a continuous structure, but rather as a discrete set of particles, generally called nanoparticles.
In this context, the organization of the particles in a periodic array is a requirement in numerous applications, such as ultra-high-density magnetic information media (ferromagnetic nanoparticles), memories based on semiconductor nanoparticles, arrays of luminescent nanoparticles or the formation of catalytic of reactional sites with very small dimensions, for example.
In these applications, and naturally in others, the organization of the particles in an array that is as perfect as possible is desirable, but very difficult to achieve in practice, in particular over sufficiently great distances.
In an attempt to respond to this requirement, it has for example been proposed to form arrays thanks to the self-organization of the particles, i.e. thanks to the interactions that occur between the particles, for example as described in the paper “Monodisperse FePt Nanoparticles and Ferromagnetic FePt Nanocrystal Superlattices” by S. Sun et al. in Science, 17 Mar. 2000 (volume 287, pages 1989-1992).
However, it is generally not possible to avoid the presence of defects (for example gaps in the array—point defects—or offsets in translation or in orientation between regions of the array—extended defects), which in practice makes it impossible to form arrays over great distances by the simple self-organization of the particles.
In an attempt to control the organization of the particles over greater distances, it has been proposed to dispose assemblies of particles constituting a part of an array in lithographed structures formed on the surface of a substrate. The paper “Templated Self-Assembly of Block Copolymers: Effect of Substrate Topography” by J. Y. Chen et al. in Adv. Mater. 2003 15, No. 19, October 2, Wiley-VCH Verlag relates to solutions of this type.
Choosing dimensions of the lithographed structures less than the distance conventionally separating two defects of the array of particles produces in each lithographed structure an assembly of particles in the form of an array that has no defects if the average distance between defects, which is a statistical datum, is respected in that assembly.
Although this technique reduces the number of defects, it cannot prevent their occurrence in certain cases. Moreover, the extent as such of the array is limited to the dimensions of the lithographed structure, the presence of which also prevents the use of the entirety of the available area.
It has also been proposed to use a substrate whose lithographed patterns interact strongly with the particles, to the point where this substrate-particle interaction predominates in controlling the location of the particles. In this solution, it is therefore the defects of the substrate, which it is naturally impossible to make perfect, that cause the defects of organization of the array (which could incidentally already be the case in the solution referred to previously).